Injection device fill volume management

ABSTRACT

An injection device including: a body including a syringe locator for receiving a syringe; and a firing mechanism including a rear cap, a plunger configured to be axially displaced in a forward direction relative to the rear cap and a driver system for driving the plunger forwards upon activation of the injection device, the firing mechanism configured to be directly or indirectly connected to the body such that an axial spacing of the rear cap and a barrel of the syringe is fixed during operation of the injection device, wherein, the firing mechanism and/or the body include first and second connection features allowing adjustment of a relative axial position of the firing mechanism and the syringe locator during assembly of the injection device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application relates to and claims priority benefits fromBritish Patent Application Serial No. 1815825.3, filed Sep. 28, 2018,and entitled “INJECTION DEVICE FILL VOLUME MANAGEMENT” the contents ofwhich are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The invention relates to injection devices for delivering a fluidsubstance to a user or patient via a syringe. In specific arrangements,the invention relates to, but need not be limited to, auto-injectors fordelivering the fluid under a force applied by a drive system.

BACKGROUND

Injection devices are used for the convenient administration ofmedicaments to patients. For example, injection devices, which may beauto-injectors, may be used for providing a single metered dose of amedicament. Such devices may be either single use “disposable” devicesin which the device is typically provided with a syringe alreadyinstalled, and which is not user-replaceable, or “reusable” devices thatallow the user to replace the syringe when the medicament has been used.

It is noted that whilst the term “syringe” is used herein for clarityand consistency, this term is not intended to be limiting. In somearrangements the syringe may for example be a cartridge (which, forexample, may be arranged to receive a disposable needle) or othermedicament container. In some arrangements thesyringe/cartridge/medicament container may be formed integrally with the(or part of the) injection device.

Injection devices may be provided in the form of an auto-injectordevice, in which delivery of the medicament is automated and the devicemay also be arranged to automate the insertion of a needle into the skinprior to the delivery of the medicament. However, it is noted that theterm auto-injector may encompass injection devices that automaticallyinsert the needle and devices which require the user to manually insertthe needle.

Injection devices generally comprise a firing mechanism that is arrangedto deliver a fluid from the syringe automatically under the force of adrive system, such as a drive spring. Optionally, injection devices mayalso comprise an insertion mechanism to displace the syringe within ahousing of the injection device to cause needle penetration. Thedelivery arrangement generally acts via a plunger which includes aplunger and may also include or engage a piston (also referred to as a“bung”) which is slidably provided within the syringe.

Injection devices may be designed and manufactured to accommodatedifferent syringes. This provides a device that may be adapted to carryand operate syringes with different features and/or characteristics,such as different fill volumes. It is desirable to improve the safetyand operability of such devices.

SUMMARY

Different syringes may be filled with different volumes of fluid, suchas medicament. A difference in fill volume of a syringe results in adifferent axial position of the bung prior to use of the syringe as itis the bung that sets the useable volume within the barrel of thesyringe. A different axial position of the bung prior to use of thesyringe may also be as a result of a differently dimensioned syringebarrel. The inventors have realised that where a gap exists between anend of the plunger and the bung, e.g. because the fill volume isrelatively low or the syringe barrel has a relatively large diameter,the plunger moves in free space for a distance before engaging the bung.This movement in free space can cause the plunger to accelerate tovelocities that are too high, such that when the plunger contacts thebung, damage may be caused to the syringe and discomfort may be causedto the recipient of an injection.

Methods and apparatus disclosed herein may be arranged to mitigate orsolve one or more problems associated with the art, including thosementioned above and/or elsewhere herein.

According to the invention in an aspect, there is provided an injectiondevice comprising: a body comprising a syringe locator for receiving asyringe; and a firing mechanism comprising a rear cap, a plungerconfigured to be axially displaced in a forward direction relative tothe rear cap and a driver system for driving the plunger forwards uponactivation of the injection device, the firing mechanism configured tobe directly or indirectly connected to the body such that an axialspacing of the rear cap and a barrel of the syringe is fixed duringoperation of the injection device, wherein, the firing mechanism and/orthe body comprise first and second connection features allowingadjustment of a relative axial position of the firing mechanism and thesyringe locator during assembly of the injection device.

The ability to alter relative axial position of the firing mechanism andthe syringe locator alters the relative axial position of a forward endof the plunger and a bung located within the syringe. The relative axialposition may be controlled to minimise an axial distance between theforward end of the plunger and the bung based, for example, on fillvolume of the syringe or tolerance in bung position of a prefilledsyringe.

Optionally, the firing mechanism comprises the first connection featuresand the body comprises the second connection features.

Optionally, the body comprises a rear portion and a forward portionaxially moveable relative to each other, and wherein the rear portioncomprises the first connection features and the forward portioncomprises the second connection features.

Optionally, one of the first and second connection features comprises athread and the other of the first and second connection featurescomprises a thread engagement member.

Optionally, one of the first and second connection features comprise aplurality of recesses at a plurality of axial positions, and the otherof the first and second connection features comprises a lug, wherein theplurality of recesses are configured to receive the lug.

Optionally, the recesses extend laterally from an axially extendingchannel, and wherein lug is configured to enter one of the plurality ofrecesses on relative rotation between the first and second connectionfeatures.

Optionally, the injection device further comprises a retention featureon one of the plurality of recesses and/or the lug.

Optionally, the retention feature comprises biasing member configured tobias the lug towards engagement with the plurality of recesses.

Optionally, the retention feature comprises a catch on one of theplurality of recesses and/or the lug configured to engage acorresponding feature on the other of the plurality of recesses and/orthe lug.

Optionally, one of the first and second connection features comprises aplurality of abutment surfaces at a plurality of axial positions, andthe other of the first and second connection features comprises afurther abutment surface configured to abut one of the abutment surfacesto prevent forward axial movement.

Optionally, the abutment surfaces are in a stepped arrangement, arelative rotational position of the one of the first and secondconnection features determining which of the plurality of abutmentsurfaces the further abutment surface will abut.

Optionally, the one of the first and second connection features furthercomprising a plurality of axial channels having a plurality of lengths,the abutment surfaces being formed by a forward end of the plurality ofchannels.

Optionally, the injection device further comprises a lock out deviceconfigured to lock the first and second connection features and therebythe relative axial position of the firing mechanism and the syringelocator.

Optionally, the driver system comprises a compression spring for acting,directly or indirectly, against the rear cap and the plunger to drivethe plunger axially forwards with respect to the rear cap.

Optionally, the plunger is telescopically received within an axiallyextending elongate member of the rear cap and forms a cylinder, andwherein the compression spring is received within the plunger for actingagainst the rear cap and the plunger.

Optionally, the firing mechanism is located in the rear portion and thesyringe locator is in the forward portion, the first and secondconnection features allowing adjustment of the relative axial positionof the rear portion and the forward portion.

Optionally, one of the forward portion and the rear portion istelescopically received within the other of the forward portion and therear portion.

According to the invention in an aspect, there is provided an injectiondevice according to any described herein and comprising a syringe orsafety syringe positioned within the body.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will be described herein with reference to theaccompanying drawings, in which:

FIG. 1 is an exploded view of an auto-injector;

FIG. 2 is a section through an auto-injector with a syringe fittedtherein;

FIG. 3 is a perspective view of a firing mechanism for an injectiondevice;

FIGS. 4 to 7 are schematic representations of exemplary rear assemblies;

DETAILED DESCRIPTION

Generally, disclosed herein are methods and apparatus for controlling agap between a bung of a syringe and a forward end of a plunger prior toactivation of an injection device. For the remainder of this document,the term “auto-injector” will be used in place of “injection device” inorder to aid description of some specific embodiments. However, thisshould not be seen as limiting.

In the following embodiments, the terms “forward” and “front” refer tothe patient facing end of the injection device or component thereof. Inother words, the front end of the injection device is the end proximalto the injection site during use. Likewise, the term “rear” refers tothe non-patient end of the injection device assembly or componentthereof. In other words, the term “rear” means distant or remote fromthe injection site during use. Further, the term axial is used toencompass a direction along or parallel to a longitudinal axis of theinjection device.

Many features of the exemplary arrangements disclosed herein aredescribed as being “coupled” to other features. This term encompassesany coupling that results in the coupled features moving together in anydirection, whether that be on a 1:1 basis or on some geared basis. Theterm “coupled” also encompasses any one of a connection betweenfeatures, an abutment of one feature against another and an engagementof one feature with another, and such coupling may be direct or may beindirect, i.e. with a third feature therebetween.

FIG. 1 shows an exploded view of an auto-injector 100. The auto-injector100 comprises a firing mechanism 102. The firing mechanism 102 comprisesa rear cap 104 and a plunger 106. The rear cap 104 comprises a head 108and an elongate member 110. The rear cap 104 and the plunger 106 areconnected to each other such that before firing, relative axial movementbetween them is resisted or prevented. The connection between the rearcap 104 and the plunger 106 is releasable such that after activation ofthe auto-injector 100, relative axial movement between them ispermitted. The nature of the releasable connection is discussed in moredetail below and may be set at assembly.

The firing mechanism 102 also comprises a biasing member 112, whichforms at least part of a drive system for driving the plunger 106axially forwards and into a barrel of a syringe (shown in FIG. 2 )retained within the auto-injector 100. In one example the biasing member112 is a drive spring (e.g. a compression spring) and will be referredto as such throughout, although this should not be construed as limitingand the skilled person will appreciate that other means may be used todrive the plunger forwards.

In the example of FIG. 1 , the plunger 106 is telescopically receivedwithin the elongate member 110 of the rear cap 104. The drive spring 112is positioned between the rear cap 104 and the plunger 106 such thatthey are biased in opposite axial directions relative to each other. Anexample of this is best shown in FIG. 2 , which is a section through anauto-injector 100 in an assembled state before activation and with asyringe 200 retained therein. The plunger 106 is received within theelongate member 110. The plunger is a hollow tube with an open end atthe rear and the drive spring 112 is received within the plunger 106. Afirst end of the drive spring 112 abuts a forward end of the plunger 106and a second end of the drive spring 112 is coupled to (i.e. abuts or isconnected to) the rear cap 104 or a further member directly orindirectly axially coupled to the rear cap 104. In the example of FIG. 2, the drive spring 112 is coupled to an end of dose indicator 114, theoperation of which is outside the scope of this description, and whichin turn is coupled to the rear cap 104. Expansion of the drive spring112 drives the plunger 106 forwards into the barrel of the syringe 200because, in the example of FIG. 1 , the position of the rear cap 104 isfixed.

In FIG. 2 , a forward end of the plunger is shown abutting a bung 202.This will not always be the case, as discussed above.

The auto-injector 100 also comprises a clutch 116, which is positionedaround the elongate member 110. Before activation of the auto-injector100, the clutch 116 is rotationally coupled to the plunger 106. Rotationof the clutch 116 therefore causes rotation of the plunger 106. Asexplained below, on activation of the auto-injector 100, the clutch 116rotates, thereby rotating the plunger 106 relative to the rear cap 104to release the connection therebetween. Operation of the clutch 116 isexplained in more detail below.

The auto-injector 100 also comprises a main body 118, which houses thefiring mechanism 102, the syringe 200 and other features necessary foroperation of the auto-injector 100. As discussed below, the main body118 may comprise a plurality of separate parts. The main body 118comprises a syringe locator, which in exemplary arrangements comprisesone or more features for receiving and optionally retaining a syringe inposition within the main body 118.

The auto-injector 100 also comprises a lockout spring 120 and lockoutshroud 122, wherein the lockout spring 120 is configured on releasethereof to displace the lockout shroud 122 axially forwards to cover aneedle of the syringe. A cap 124 also forms part of the auto-injectorand covers a needle or forward end of the auto-injector prior to use.

In exemplary arrangements, a rear assembly of the auto-injector may beformed from the firing mechanism 102 and a rear portion of the main body118.

FIG. 3 shows a perspective view of an assembly 300 for a firingmechanism. The assembly 300 comprises the rear cap 104 and the plunger106. The plunger 106 is telescopically received within the elongatemember 110. The assembly 300 may also comprise an end of dose indicator114, but as explained above, the operation of that feature is beyond thescope of this description.

The exemplary plunger 106 comprises a cylindrical tube that is open at arear end and closed at a forward end. The forward end of the plunger 106comprises a shoulder 302 and a projection 304 configured to engage abung 202 in a syringe barrel. In the example shown in FIG. 3 , theplunger 106 also comprises a plunger release lug 306 configured toengage with a plunger release recess 308 in the elongate member 110. Inthe exemplary arrangements of FIG. 3 the lug 306 extends radially froman outer surface of the plunger 106.

The elongate member 110 comprises an axially extending plunger releasechannel 310. The recess 308 is formed in a sidewall of the channel 310.That is, the recess 308 extends circumferentially (or transverse to theaxial channel) around the outer of the elongate member 110. It is notedthat while only one recess 308 is shown in FIG. 3 , more recesses may beprovided in the elongate member 110 at different axial positions. Therecess 308 is configured to receive the lug 306 of the plunger 106. FIG.3 shows the lug 306 received in the recess 308.

The axial channel 310 and the recess 308 are configured such thatrotation of the plunger 106 relative to the elongate member 110 in afirst direction moves the lug 306 into the recess 308 and rotation in asecond, opposite direction moves the lug 306 out of the recess 308. Asdiscussed above, rotation of the plunger 106 may be provided by rotationof the clutch 116, which is rotationally coupled to the plunger 106.

FIGS. 4 a and 4 b show a schematic representation of a section throughan injection device 400. The exemplary arrangement of FIGS. 4 a and 4 ballow for the connection of the firing mechanism to the body to becontrolled to allow adjustment of a relative axial position between thefiring mechanism, and more specifically a forward end of the plungerrod, and the syringe locator during assembly of the injection device.This controls a start position of the forward end of the plunger onactivation of the injection device 400. Specifically, when a syringe isfitted to the injection device, the start position of the forward end ofthe plunger relative to the bung of the syringe is controlled.

The injection device 400 comprises a firing mechanism 402. The firingmechanism 402 may comprise one or more of the features of the firingmechanism 300 shown in FIG. 3 and described above. As shown in FIG. 4 ,the firing mechanism 402 comprises a plunger 404 and a rear cap 406. Therear cap comprises an elongate member 408 into which the plunger 404 istelescopically received. A drive spring 410 is received within theplunger 404 and acts against in opposed directions the plunger 404 andthe rear cap 406. The skilled person will appreciate that the specificfiring mechanism configuration shown in FIG. 4 is not essential to theinvention and that other firing assemblies may be used.

In the arrangement of FIGS. 4 a and 4 b (and indeed of FIGS. 5 to 7 ),the firing mechanism 402 is connected to a rear portion 412 a a body 412and the syringe locator (and therefore the syringe, when in use) isconnected to or forms part of a forward portion 412 b of the body 412.

In the example, the firing mechanism 402 is in fixed connection with therear portion 412 a after assembly and optionally there is only a singleconnection point. That is, in the example shown the firing mechanism 402is always assembled in the same relative axial position to the rear body412 a. However, it will be understood by the skilled person that thefeatures of any other embodiment described herein may be incorporatedinto the arrangement of FIGS. 4 a and 4 b , as appropriate. Accordingly,the axial position of the firing mechanism 402 within the rear portion412 a may be controlled as set out herein and this may be in combinationwith the features described below.

The relative axial position of the firing mechanism 402 in the rearportion 412 a to the syringe locator in the forward portion 412 b iscontrolled by first and second connection features, which in thisexample comprise a threaded connection 414 between the rear portion 412a and the forward portion 412 b. That is, one of the first and secondconnection features comprises a thread and the other of the first andsecond features comprises a thread engagement member, which may be a lugor another, corresponding thread.

In FIG. 4 , the first and second connection features are located on theforward and rear portions 412 a, 412 b of the body 412. In otherarrangements, one of the first and second connection features may belocated on the rear portion 412 b of the body 412, and the other of thefirst and second connection features may be located on the firingmechanism. This is generally true of the exemplary arrangements in FIGS.5-7 also.

The threaded connection 414 comprises a thread on the rear portion 412 band a corresponding thread engagement feature on the forward portion 412a. The skilled person will appreciate that these may be oppositelyconfigured.

The forward portion 412 b is telescopically received within the rearportion 412 a (although this may be oppositely configured) and thedistance by which it is received is controlled by the threadedconnection 414.

FIG. 4 a shows the forward portion 412 b received within the rearportion 412 a by a first distance, and FIG. 4 b shows the forwardportion 412 b received within the rear portion 412 a by a seconddistance greater than the first distance. This is achieved by increasedrotation of the rear portion 412 b relative to the forward portion 412 aand the corresponding. This allows control of the relative axialdistance between the firing mechanism 402 and a syringe located withinthe syringe locator. The arrangement of FIG. 4 b has a reduced axialdistance between the two when compared to the axial distance shown inFIG. 4 a.

As with the exemplary arrangement of FIGS. 6 a-c and 7 a-c describedbelow, the sheath 420 may comprise an angled surface 416 to interactwith a lug 418 of the plunger 404 to displace it laterally at any axialposition, based on the configuration of the threaded connection 414.Accordingly, the rotational alignment of the firing mechanism 402, andtherefore the lug 418, may be controllable. For example, an end blank422 may be rotatable and rotationally coupled to the firing mechanism402 to select a rotational alignment of the firing mechanism 402relative to the body 412 and therefore the sheath 420. Alternatively, aclutch arrangement may be used as described herein.

FIG. 5 shows an alternative arrangement of an injection device 500allowing the connection of the firing mechanism to the body to be set atone of a plurality of relative axial alignments during assembly of theinjection device. This in turn allows adjustment or control over arelative axial position of the firing mechanism and the syringe locator.

A firing mechanism 502 is shown only schematically, although thearrangements disclosed above may be used. The firing mechanism 502comprises a plunger 504 and a rear cap 506. The rear cap 506 comprisesone or more lugs 508. The lug 508 extends radially outwards. A body 512comprises a forward portion 512 a and a rear portion 512 b. In theexample of FIG. 5 , the rear portion 512 b comprises first connectionfeatures, which further comprise a plurality of recesses 510 at aplurality of axial positions on the body. The recesses 510 areconfigured to receive second connection features, which comprise the oneor more lugs 508 to prevent relative axial movement between the firingmechanism 502 and the body 512. In the example shown in FIG. 5 , therecesses 510 extend laterally on an inner wall of the body 512. That is,the recesses 510 extend transverse to the axial direction of theinjection device 500. In such arrangements, the lug 508 may enter one ofthe recesses 510 on relative rotation of the firing mechanism 502 andthe body 512.

In the example shown in FIG. 5 , the body 512 also comprises an axialchannel 514 from which the recesses 510 extend. The axial channel 514 isconfigured to receive the lug 508 and allow axial movement of the firingmechanism 502.

In addition, the recesses 510 and/or the lug 508 may include a retentionfeature. The retention feature may retain the lug 508 in the recess 510into which it has entered. The retention feature may take any of anumber of forms, such as a snap fit arrangement, a catch and/or abiasing member configured to bias the lug 508 towards the recess 510,optionally in cooperation with one or more angled surfaces.

On assembly of the injection device, the firing mechanism 502 isreceived within the body 512 until the lug 508 is received within thechannel 514 and moved axially until it is aligned with a selected one ofthe recesses 510. The firing mechanism 502 is then rotated relative tothe body 512 to cause the lug 508 to enter the recess 510.

In an alternative arrangement, the second connection features compriseone or more sprung lugs and the first connection features comprise aplurality if recesses at different axial positions. The sprung lugs maybe configured to ride over the body until they are located within thecorrect recess.

In a further embodiment, the forward portion 512 a may be telescopicallyreceived within the rear portion 512 a and the second connection feature(i.e. the lug 508) may be positioned on the forward portion 512 b asopposed to the firing assembly 502. The second connection feature (i.e.the channel 514 and the recesses 510) are located on the rear portion512 b and are configured to engage with the lug 508 on the forwardportion 512 a and may therefore be positioned forwards of the positionshown in FIG. 5 and optionally at a forward end of the rear portion 512b. The position of the firing assembly 502 within the rear portion 512 bmay be fixed. This arrangement is similar to the arrangement of FIGS. 4,6 and 7 , except that the connection between the forward portion 512 aand the rear portion 512 b is controlled by receipt of the lug 508,which is formed on the forward portion 512 a, within the channel 510 andsubsequently one of the recesses 510.

FIGS. 6 a-c show a further exemplary arrangement of an injection device600. The injection device 600 is configured to allow the connection of afiring mechanism to a body to be set at one of a plurality of relativeaxial alignments during assembly of the injection device.

In the exemplary arrangement of FIG. 6 , the firing mechanism 602comprises a rear cap 604, a plunger 606 and a drive system, which inthis case comprises a compression spring 608. The rear cap 604 isconfigured to retain the plunger 606 against a bias applied by thecompression spring 608, such retention being releasable on operation onthe injection device 600, as explained above. First connection featurescomprise a guide member 610 located on the firing mechanism 602 and thatis configured to align with second connection features, which comprisecorresponding guide features on a body 612 of the injection device 600.The guide features 614 on the body 612 comprise a plurality of abutmentsurfaces, each at different axial locations on the body 612. In theexample shown in FIG. 6 , the abutment surfaces for a steppedarrangement. The guide feature 610 of the firing mechanism 602 comprisesa protrusion from the rear cap 604, although other forms of guidefeature are possible.

During assembly, the firing mechanism 602 is located within the body612. The rotational alignment of the firing mechanism 602 relative tothe body 612 determines which of the abutment surfaces the guide feature610 of the firing mechanism 602 will rest on. In FIG. 6 b , the guidefeature 610 rests on a first abutment surface and in FIG. 6 c , theguide feature 610 rests on a second abutment surface further forwardthan the first abutment surface. Therefore, the relative axial positionof the firing mechanism 602 and the syringe locator of the body 612 maybe controlled.

The injection device 600 also comprises an end blank 618 that may befitted into a rear end of the device after location of the firingmechanism 602. The end blank 618 comprises a plurality of featuresconfigured to align with the guide features 614 of the body 612. The endblank 618 retains the firing mechanism 602 in the selected axialposition.

In the example of FIGS. 6 a-c , the plunger 606 comprises a lug 616 thatis located in a recess of the rear cap 604 while the plunger 606 isbeing retained. Relative rotation between the plunger 606 and the rearcap 604 disengages the lug 616 from the recess and allows thecompression spring 608 to drive the plunger 606 forwards. In the exampleshown in FIGS. 6 a-c , the sheath 620 may be configured to cause thatrelative rotation of the plunger 606. In specific examples, the sheath620 may comprise an angled surface configured to displace the lug 616laterally on rearward displacement of the sheath 620. As can be seen inFIGS. 6 b and 6 c , the axial position of the lug may be changed withthe axial position of the firing mechanism 602. Therefore, the sheath620 may be configured to laterally displace the lug 616 at each of thepossible axial positions. Accordingly, the angled surface of the sheath620 may be arranged to interact with the lug at different axialpositions and also at different rotational alignments with the sheath620 (and the body 612). That is, as the firing mechanism 602 is rotatedto abut the correct abutment surface, the rotational position of the lug616 is altered. Therefore, the angled surface of the sheath 620 may beconfigured to displace the lug 616 at different axial positions based onthe rotational position of the lug 616. In some arrangements, the sheath620 may comprise a plurality of angled surfaces corresponding to theabutment surfaces, wherein each angled surface is configured to displacethe lug 616 laterally when the guide feature 610 of the firing mechanism602 abuts one of the abutment surfaces. In other arrangements, a clutchmay be used, as described herein, wherein the clutch is coupled to thesheath 620 such that rearward axial displacement of the sheath causesrotation of the clutch irrespective of the axial position of the firingmechanism 602. The clutch may be rotationally coupled to the syringeplunger to cause lateral displacement of the lug 616.

FIGS. 7 a-c show a further exemplary injection device 700. In theexemplary arrangement of FIGS. 7 a-c , a firing mechanism 702 comprisesa rear cap 704, a plunger 706 and a drive system, which in this casecomprises a compression spring 708. The rear cap 704 is configured toretain the plunger 706 against a bias applied by the compression spring708, such retention being releasable on operation on the injectiondevice 700, as explained above. In the arrangement of FIGS. 7 a-c , thefiring mechanism 702 is connected to a rear portion 712 a of the body712 and the syringe locator (and therefore the syringe, when in use) isconnected to or forms part of a forward portion 712 b of the body 712.

In the example, of FIGS. 7 a-c , the firing mechanism 702 is in fixedconnection with the rear portion 712 a after assembly and there is onlya single connection point. That is, the firing mechanism 702 is alwaysassembled in the same relative axial position to the rear body 712 a.However, it will be understood by the skilled person that the featuresof any other embodiment described herein may be incorporated into thearrangement of FIGS. 7 a-c , as appropriate. Accordingly, the axialposition of the firing mechanism 702 within the rear portion 712 a maybe controlled as set out herein and this may be in combination with thefeatures described below.

The relative axial position of the firing mechanism 702 in the rearportion 712 a to the syringe locator in the forward portion 712 b iscontrolled by first and second connection features 722 on the body 712that allow control of the relative axial position of the rear portion712 a to the forward portion 712 b. The connection features 722 comprisefirst connection features 722 a that are configured to cooperate withsecond connection features 722 b.

The rear portion connection features 722 a comprise at least oneinternal protrusion 724 that is configured to be received with any of aplurality of recesses 726 forming part of the rear portion connectionfeatures 722 b. It will be understood that the at least one internalprotrusion and the recesses may be on one or both of the rear portion712 a and the forward portion 712 b. In the exemplary arrangement ofFIGS. 7 a-c , each of the rear portion connection features 722 a and theforward portion connection features 722 b comprises a plurality ofinternal protrusions 724 and a plurality of recesses 726. Further, theprotrusions and recesses extend at least partially, and in onearrangement fully, around an inner circumference of the rear portion 712a and an outer circumference of the forward portion 712 b.

The forward portion 712 b is telescopically received within the rearportion 712 a (although this may be oppositely configured) and thedistance by which it is received is controlled by the connectionfeatures 722.

FIG. 7 b shows the forward portion 712 b received within the rearportion 712 a by a first distance, and FIG. 7 c shows the forwardportion 712 b received within the rear portion 712 a by a seconddistance greater than the first distance. This allows control of therelative axial distance between the firing mechanism 702 and a syringelocated within the syringe locator. The arrangement of FIG. 7 c has areduced axial distance between the two when compared to the axialdistance shown in FIG. 7 b.

The skilled person will be able to envisage a number of other connectionfeatures to connect the rear portion 712 a to the forward portion 712 band the example given in FIGS. 7 a-c is not limiting. For example, theconnection features may comprise a threaded arrangement on the rearportion 712 a and the forward portion 712 b. Alternatively, theconnection features may comprise sprung loaded protrusions and aplurality of recesses. The above are merely examples and should not beconstrued as limiting.

As with the exemplary arrangement of FIGS. 6 a-c , the sheath 720 maycomprise an angled surface 714 to interact with a lug 716 of the plunger706 to displace it laterally at a plurality of axial positions, based onthe configuration of the connection features 722 a, 722 b. Accordingly,the rotational alignment of the firing mechanism, and therefore the lug716, may be controllable. For example, an end blank 718 may be rotatableand rotationally coupled to the firing mechanism 702 to select arotational alignment of the firing mechanism 702 relative to the body712 and therefore the sheath 720. Alternatively, a clutch arrangementmay be used as described herein.

Once assembled, the user has no control over the relative axial positionof the firing mechanism compared to the body. Any of the rear assembliesdisclosed herein may also comprise a lock that may be activated to lockthe axial position of the rear cap relative to the body.

Operation of the auto-injector 100 is described below using thereference numerals of the exemplary arrangement shown in FIGS. 1 and 2 .Any of the arrangements of the rear assembly described above may beused.

In use, a user removes the cap 124 of the auto-injector 100, which inturn removes a rigid needle shield covering the needle. Removal of thecap exposes the lockout shroud 122, which protrudes from a forward endof the body 118.

The user places a forward end of the lockout shroud 122 against aninjection site and pushes the auto-injector 100 downwards onto theinjection site. This action pushes the lockout shroud 122 rearwardswithin the auto-injector 100. The lockout shroud interacts with theclutch 116 to rotate it. This may be done by forcing a surface (or pip)of the lockout shroud 122 against an angled surface on the clutch 116,which translates the rearward motion of the lockout shroud 122 intorotational motion of the clutch 116.

As the clutch 116 is rotationally coupled to the plunger 106, rotationof the clutch 116 causes rotation of the plunger 106. In somearrangements, the clutch 116 may have an internal track located on aninternal wall thereof and that receives a lug of the plunger 106. Thelug may be the same as the lug 306 described with reference to FIG. 3 .Rotation of the plunger 106 with respect to the rear cap 104 releasesthe connection between the rear cap 104 and the plunger 106, allowingthe plunger 106 to be driven forwards under force of the drive spring112. In the examples of FIGS. 1-3 , this is provided by rotating the lug306 of the plunger 106 out of the recess 308 the lug 306 is positionedin at assembly and into the axial channel 310. The lug 306 is therebyallowed to travel forwards within the channel 310.

The drive spring 112 then acts against the plunger 106 and the rear cap104. Because the rear cap 104 is fixed within the auto-injector 100, theforce delivered by the drive spring 112 acts to drive the plunger 106into the barrel of the syringe. Because the gap between the forward endof the plunger 106 and the bung 202 has been controlled during assembly,the plunger 106 does not accelerate above a safe velocity that wouldrisk damage to the syringe 200 or harm or discomfort to the subject ofthe injection.

After delivery of the contents of the syringe 200, the lockout shroud isdeployed under force of the lockout spring 120 in any of a number ofways that will be apparent to the skilled person.

The skilled person will be able to envisage other assemblies,auto-injectors and features thereof without departing from the scope ofthe appended claims. In particular, it is noted that one or morefeatures included in one or more drawings may be integrated intoauto-injectors shown in other drawings, as will be appreciated by theskilled person.

The invention claimed is:
 1. An injection device comprising: a bodycomprising a syringe locator for receiving a syringe; and a firingmechanism configured to deliver a fluid from the syringe, the firingmechanism comprising a rear cap, a plunger configured to be axiallydisplaced in a forward direction relative to the rear cap and a driversystem for driving the plunger forwards upon activation of the injectiondevice, the firing mechanism configured to be directly or indirectlyconnected to the body such that an axial spacing of the rear cap and abarrel of the syringe is fixed during operation of the injection device,wherein, the firing mechanism and/or the body comprise first and secondconnection features allowing adjustment of a relative axial position ofthe firing mechanism and the syringe locator during assembly of theinjection device.
 2. The injection device according to claim 1, whereinthe firing mechanism comprises the first connection features and thebody comprises the second connection features.
 3. The injection deviceaccording to claim 2, wherein one of the first and second connectionfeatures comprises a thread and the other of the first and secondconnection features comprises a thread engagement member.
 4. Theinjection device according to claim 2, wherein the rear cap comprisesthe first connection features.
 5. The injection device according toclaim 2, wherein the body comprises a rear portion and a forwardportion, and wherein the rear portion comprises the second connectionfeatures.
 6. The injection device according to claim 1, wherein the bodycomprises a rear portion and a forward portion axially moveable relativeto each other, and wherein the rear portion comprises the firstconnection features and the forward portion comprises the secondconnection features.
 7. An injection device according to claim 6,wherein the firing mechanism is located in the rear portion and thesyringe locator is in the forward portion, the first and secondconnection features allowing adjustment of the relative axial positionof the rear portion and the forward portion.
 8. The injection deviceaccording to claim 7, wherein one of the forward portion and the rearportion is telescopically received within the other of the forwardportion and the rear portion.
 9. The injection device according to claim6, wherein one of the first and second connection features comprises athread and the other of the first and second connection featurescomprises a thread engagement member.
 10. The injection device accordingto claim 1, wherein one of the first and second connection featurescomprises a thread and the other of the first and second connectionfeatures comprises a thread engagement member.
 11. The injection deviceaccording to claim 1, wherein one of the first and second connectionfeatures comprise a plurality of recesses at a plurality of axialpositions, and the other of the first and second connection featurescomprises a lug, wherein the plurality of recesses are configured toreceive the lug.
 12. The injection device according to claim 11, whereinthe recesses extend laterally from an axially extending channel, andwherein the lug is configured to enter one of the plurality of recesseson relative rotation between the first and second connection features.13. The injection device according to claim 11, further comprising aretention feature on one of the plurality of recesses and/or the lug.14. The injection device according to claim 13, wherein the retentionfeature comprises a catch on one of the plurality of recesses and/or thelug configured to engage a corresponding feature on the other of theplurality of recesses and/or the lug.
 15. The injection device accordingto claim 11, wherein receipt of the lug in one of the plurality ofrecesses prevents relative axial movement between the firing mechanismand the body.
 16. The injection device according to claim 1, wherein oneof the first and second connection features comprises a plurality ofabutment surfaces at a plurality of axial positions, and the other ofthe first and second connection features comprises a further abutmentsurface configured to abut one of the abutment surfaces to preventforward axial movement.
 17. The injection device according to claim 16,wherein the abutment surfaces are in a stepped arrangement, a relativerotational position of the one of the first and second connectionfeatures determining which of the plurality of abutment surfaces thefurther abutment surface will abut.
 18. The injection device accordingto claim 16, the one of the first and second connection features furthercomprising a plurality of axial channels having a plurality of lengths,the abutment surfaces being formed by a forward end of the plurality ofchannels.
 19. The injection device according to claim 1, furthercomprising a lock out device configured to lock the first and secondconnection features and thereby the relative axial position of thefiring mechanism and the syringe locator.
 20. The injection deviceaccording to claim 1, wherein the driver system comprises a compressionspring for acting, directly or indirectly, against the rear cap and theplunger to drive the plunger axially forwards with respect to the rearcap.
 21. The injection device according to claim 20, wherein the plungeris telescopically received within an axially extending elongate memberof the rear cap and forms a cylinder, and wherein the compression springis received within the plunger for acting against the rear cap and theplunger.
 22. The injection device according to claim 1 furthercomprising a syringe positioned within the body.
 23. The injectiondevice according to claim 1, wherein the driver system is configured topush against the rear cap to drive the plunger forwards upon activationof the injection device.